Paul Kantner, the founding rhythm guitarist of Jefferson Airplane and Jefferson Starship, died Thursday, January 28, in San Francisco. He was 74.

Kantner died of multiple organ failure and septic shock after suffering a heart attack earlier this week, according to the San Francisco Chronicle. The paper noted that he had survived a heart attack in March 2015 as well.

As a founding member of Jefferson Airplane, Kantner was a pioneer of the mid-to-late-Sixties rock scene in San Francisco. Along with the Grateful Dead, Big Brother and the Holding Company, Moby Grape and Quicksilver Messenger Service, Jefferson Airplane were one of the most significant Bay Area groups to emerge during that time. Their 1967 album, Surrealistic Pillow, was a signature recording of the psychedelic rock era and featured two of the period’s biggest hits, “Somebody to Love” and “White Rabbit.”

With his blond hair and wire-frame eyeglasses, Kantner cut a distinctive figure in the group, performing during their Sixties prime with a Rickenbacker 360/12. Although lead vocalists Marty Balin and Grace Slick took the spotlight, it was Kantner who eventually became the group’s leader, seeing Jefferson Airplane through its reinvention as a hard rock act in the late Sixties and onward to its rebirth as Jefferson Starship in 1974, a group he led until his death.

Robby Krieger and John Densmore of the Doors, Jefferson Airplane’s Sixties contemporaries from Los Angeles, paid tribute to Kantner on Thursday night. “Our condolences go out to the friends, family and fans of Paul Kantner of Jefferson Airplane on the news of his passing,” the surviving Doors members wrote on their Facebook page. “Music would not be the same without the sounds of The Doors and Jefferson Airplane, which both contributed so heavily to the signature sound of the Sixties and Seventies.”

Paul Lorin Kantner was born in San Francisco on March 17, 1941. As a youngster, he became a fan of science fiction and found in it an escape from his experience at a Jesuit military boarding school. The emerging rock and roll scene of the Fifties gave him yet another escape, as well as a format in which to revolt against authority.

Taking up the guitar, Kantner fell in with the Bay Area folk scene in the early Sixties. For a brief period in 1964 he moved to Los Angeles, where he worked in a folk duo with David Freiberg, who would go on to form Quicksilver Messenger Service and later, in the Seventies, work again with Kantner after both men had found success.

In the summer of 1965, Kantner was performing at the Drinking Gourd, a San Francisco folk club, when a singer and guitarist named Marty Balin invited him to form a new band. Inspired by the folk-rock successes of the Byrds and Simon & Garfunkel, Balin hoped to create a new act that would follow in their style. He had purchased a former pizza parlor on San Francisco’s Fillmore Street that he converted into a music club, called the Matrix, which would serve as the group’s home base.

With Kantner onboard, the duo began recruiting other musicians. Their bandmates eventually included Kantner’s friend, blues guitarist Jorma Kaukonen, and bassist Jack Casady. For a brief period, their drum chair was held by Skip Spence, a guitarist who would soon go on to form Moby Grape. For their singer, they selected Signe Toly Anderson, whom Balin had also seen perform at the Drinking Gourd.

Together, they took the name Jefferson Airplane, an unusual moniker influenced by the then-thriving blues scene. According to Kaukonen, the name was a parody of blues artists’ names—in particular Blind Lemon Jefferson—dreamed up by his friend Steve Talbot.

“I had this friend in Berkeley who came up with funny names for people,” Kaukonen recalled. “His name for me was Blind Thomas Jefferson Airplane. When the guys were looking for band names and nobody could come up with something, I remember saying, ‘You want a silly band name? I got a silly band name for you!’”

Their 1966 debut album, Jefferson Airplane Takes Off, was a folk-rock affair, and though it failed to make much impact, the newly launched rock magazine Crawdaddy! featured the disc on the cover of its January 1967 issue, calling the record “the most important album of American rock” released in 1966. By then, Spence had left and was replaced by drummer Spencer Dryden. Anderson had also left the previous May to raise her daughter. In her place was a new and powerful singer named Grace Slick, whom the group had known from her previous band, the Great Society.

It was this lineup that would go on to find success in 1967 with Surrealistic Pillow. From its title to its cover art and entrancing guitar tones, the album exemplified the psychedelic rock genre and helped establish it with the hits “Somebody to Love” and “White Rabbit.” The album’s title had been suggested by Grateful Dead guitarist Jerry Garcia, who produced the disc, although he was credited on it as “spiritual advisor.”

It was with the group’s third album, 1967’s After Bathing at Baxter’s, that Kantner began to shape Jefferson Airplane’s sound and musical direction. Along with Slick, Kantner composed most of the album’s tracks, moving away from Balin’s ballad-like compositions and toward a harder sound and more improvisational approach influenced by Jimi Hendrix and the emerging hard rock scene. The lyrics, too, were reflecting more socially-conscious themes, filtered through Kantner’s and the group’s use of LSD.

Asked by Rolling Stone in 1970 about his reason for making music, Kantner replied, “Trying to make consciousness. Pointing things out. Just make people enjoy themselves.

“We didn’t even know what we were doing when we started doing it. Looking back, all we were saying was, ‘Look, we’re having a good time.’ And nothing else. Just sitting around having a good time with all this shit going on around us. Pretty soon people start filtering in, saying, ‘Hey, they’re having a good time.’”

Though Jefferson Airplane would perform at three of the Sixties’ most significant musical events—Monterey Pop, Woodstock and the ill-fated Altamont Free Concert—they would never again enjoy the success of Surrealistic Pillow. By 1970, the group was beginning to fall apart. Kantner’s sci-fi-inspired “Have You Seen the Saucers” was a notable single for the group in 1970 and marked the start of a theme he would explore in his solo albums, beginning with Blows Against the Empire that same year.

Recorded in 1970 as a one-off project, Blows Against the Empire was credited to Paul Kantner and the Jefferson Starship. A concept album built upon a science-fiction song suite, it featured Kantner alongside Slick, Casady and guest artists that included David Crosby, Graham Nash and members of both the Grateful Dead and Santana. After Jefferson Airplane broke up in 1972, Kantner would revive the Jefferson Starship name and continue to perform and record with it until his death.

Along with Slick, Freiberg and lead guitarist Craig Chaquico, Kantner officially launched Jefferson Starship in 1974 with the album Dragon Fly. The record also featured Kantner and Slick’s former bandmate Marty Balin on one track, “Caroline.” Initially reluctant to become a full member of Jefferson Starship, Balin eventually signed on and was responsible for writing their biggest hit, “Miracles,” from 1975’s Red Octopus. The group continued to score subsequent chart successes with the songs “With Your Love,” “Count on Me” and “Runaway.”

By 1980, Kantner was the only Jefferson Airplane member left in the group He survived a cerebral hemorrhage in 1980 and continued to work with Jefferson Starship but left in 1984 under a legal agreement with the other members that forbade the use of “Jefferson” without approval of all respective members. During this period, Slick continued to perform with her own group using the name Starship and had hits with the songs “We Built This City,” “Sara” and “Nothing’s Gonna Stop Us Now.”

Kantner and Jefferson Airplane reformed in 1989 and released a self-titled album. They rejoined again in 1996 for their induction into the Rock and Roll Hall of Fame.

Kantner is survived by three children: China, Alexander and Gareth. China, born in 1971 to Kantner and Slick, is a former MTV DJ and actress. Alexander was born to Kantner and Jefferson Starship vocalist Cathy Richardson, and has played bass with Jefferson Starship. Gareth is a film producer.

Beyond his music, Kantner was an enduring symbol of the Sixties music revolution and a representative of a time when liberal thought and mindful regard for the planet were transforming society.

In his November 1970 interview with Rolling Stone, Kantner described the track “Starship,” from the then newly released Blows Against the Empire, in fanciful terms that would have been anything but unusual to rock music fans of the era.

“That’s a song, [on] side two of my album. It’s about us—me and Jerry Garcia and David Crosby stealing a starship—hijacking a spaceship, going where whoever comes along wants to go.

“It’s my answer to the ecology problem,” Kantner continued. “It’s the only way it’s all going to get together and work. Unless we have a war or a big disease or a famine, there’s just too many people, and they’re gonna have to get off the planet. This is my way of starting to get off a little earlier.”